Narrow-leaved milkweed is an erect, slender herbaceous
perennial plant growing to some 3' tall with several glabrous stems
and milky juice. The leaves are 5" long and up to 3/8"
wide, commonly folded along the midrib, linear to linear-lanceolate,
with short petioles, and usually in whorls of three to six. The
flowers are greenish-white, umbellate, with a five-merous deeply-lobed
calyx which is usually imbricate and a corolla with five spreading lobes
surrounding a raised crown made up of five concave hoods each with an
incurved exserted hornlike structure. The five stamens are fused
to form a filament column, and the anthers are united and inflexed on
a massive pistil head which is formed by the fusion of the style tips.
The fruit is a smooth, brown, narrow, sharp-pointed pod about 3-1/2"
long which splits open on one side upon maturity to release seeds 1/4"
long each with a 1-1/8" long coma of fine silky white hairs. Narrow-leaved
milkweed is a common species of dry open places mostly below 7000' in
many plant communities, blooming from June to August.